1. Field of the Invention
Embodiments described herein relate generally to a rotation angle measuring method of a multi-charged particle beam image, a rotation angle adjustment method of a multi-charged particle beam image, and a multi-charged particle beam writing apparatus, and for example, relates to a rotation angle measurement based on a rotational shift of a multi-beam image in multi-beam pattern writing and an adjustment technique thereof.
2. Related Art
A lithography technique which leads development of micropatterning of a semiconductor device is a very important process for exclusively generating a pattern in semiconductor manufacturing processes. In recent years, with an increase in integration density of an LSI, a circuit line width required for semiconductor devices is getting smaller year by year. An electron beam pattern writing technique has inherently superior resolution and a mask pattern is written to mask blanks using an electron beam.
For example, a writing apparatus using multiple beams is known. Compared with a case in which one electron beam is used, many beams can be emitted at a time by using multiple beams so that throughput can be improved significantly. In such a writing apparatus of multi-beam mode, for example, an electron beam emitted from an electron gun assembly is passed through a mask having a plurality of holes to form multiple beams, each beam is subjected to blanking control, and each beam that is not shielded is reduced by an optical system to reduce a mask image and deflected by a deflector before being shot at a predetermined position on a target object.
Here, in multi-beam pattern writing, a rotational variation of a whole multi-beam image could arise due to a distortion of the optical system, a displacement of an aperture plate array to form multiple beams from design values, and/or the Coulomb effect. If a rotational variation arises in a multi-beam image, a problem that a written pattern also has a positional displacement or a dimensional displacement arises. Thus, it is very important to measure the rotation angle of a multi-beam image on a target object surface directly affecting positional precision or dimensional precision of a pattern to be written and to adjust the rotation angle using the result thereof. However, the current amount per beam is small in multiple beams and measuring one beam after another increases a measurement error. Further, the number of beams is large and thus, it takes a very long time to adjust one beam after another, which makes it difficult to adjust each beam due to time constraints.
Regarding the measurement of rotational variation (rotation angle), a technique to measure the rotational variation of multiple beams for exposure by forming multiple beams for measurement that are not used for exposure around multiple beams for exposure used for exposure and measuring the position of the multiple beams for measurement is proposed (see Published Unexamined Japanese Patent Application No. 2004-165498, for example).